Progressive headless experience / Admin Ui functionality questions

Problem/Motivation

I find the "Acquia CMS Headless UI" does too much functionality and does NOT support a progressive headless process (where progressive means, a regular Drupal site but slowly rebuild components in NextJS / another framework).

This is because when you enable it hides things like "manage display" on entities, so it's a all or nothing approach.

I suggest adding configuration dropdown to choose progressive or headless mode.

Additionally, the appearance section for Drupal themes is hidden, this makes sense to hide front theme options, however it has a side effect of hiding admin theme options which are necessary to change the CMS editor experience.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes